Papers by Author: Guo Wei Chang

Abstract: The self-made device to test the shrinkage ratio and temperature of cast ingot is used to measure the shrinkage mass of Fe-0.1%C, Fe-0.15%C, Fe-0.33%C cast ingot with the dimension of 200×80×100mm. The results show that the total shrinkage mass of cast ingot is increased with the increase of carbon content. In the carbon content range of the experiment, the rate of shrinkage and expansion of Fe-0.15%C steel during, before and after eutectoid reaction is all the quickest. The solid-state shrinkage rate of Fe-0.15%C steel before eutectoid reaction is 288 μm•s-1. The shrinkage mass and rate of cast ingot after eutectoid reaction are 0.051 mm and 127 μm•s-1, respectively. The expansion mass and rate of cast ingot during eutectoid reaction are 0.016 mm and 53.3 μm•s-1, respectively.

Abstract: Effects of melt superheating holding time on microstructure and mechanical properties of AZ31B magnesium alloy were studied. The results show that the grain size of AZ31B magnesium alloy is gradually increased with the elongation of holding time. The grain is the finest without insulation work, and the increase amplitude of grain size is the most when holding for 20 minutes in this experiment. The higher is the melt superheating temperature, the larger the increase amplitude of grain size when holding for 20 minutes is. The tensile strength, yield strength and elongation percentage of AZ31B magnesium alloy specimens are small declined with the elongation of holding time under lower melt temperature. At 850°C or 900°C, the mechanical properties are rapidly declined with the elongation of holding time when holding time is less than 20 minutes, whereas the mechanical properties are slight increased when holding time is more than 20 minutes. DSC analysis shows that the elongation of holding time causes the increase of solidification onset temperature and the augment of solidification range, so the undercooling degree and nucleation rate are decreased in the melt, which result in the grain coarsening and the mechanical properties decrease.

Abstract: The δ→γ phase transformation in the steel was studied in detail, and the relationship between δ→γ phase transformation and the crack formation in continuous casting slabs was discussed as well. The results indicate that the micropores are formed at the positions where δ-phase transformation terminates during the δ→γ phase transformation for low-carbon non-peritectic steel. The micropores will also be formed at the positions where the peritectic reaction of the steel terminates, then the pores are remained on the grain boundary of γ-phase when γ-phase becomes granulated. The micropores distributing on the grain boundary of γ-phase is one of the results for the crack formation of continuous casting slabs and the obvious plasticity decrease of δ-phase zone in the steel. The theoretical analysis results are basically consistent with the experimental results.